RATE REDUCTION BONDS AND VARIABLE INTEREST ENTITIES - Summary of the Impact of Funding on the Income Statements (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Condensed Income Statements, Captions [Line Items]
Interest Expense on RRB Principal (included in Interest Expense)	$ 134,066	$ 135,216	$ 403,067	$ 399,654
PSNH
Condensed Income Statements, Captions [Line Items]
Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net)	7,360	20,421	39,034	39,944
Interest Expense on RRB Principal (included in Interest Expense)	14,942	16,378	44,029	44,654
PSNH | VIE | Rate Reduction Bonds
Condensed Income Statements, Captions [Line Items]
Amortization of RRB Principal (included in Amortization of Regulatory Assets, Net)	10,800	10,800	32,400	32,200
Interest Expense on RRB Principal (included in Interest Expense)	$ 4,900	$ 5,200	$ 14,900	$ 15,900